Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $64.58   4.211%   $67.2995   $67.30   $67.30   $67.30  
  Purchase #2 $8.45   9.540%   $9.2561   $9.26   $9.25   $9.30  
  Purchase #3 $58.61   6.830%   $62.6131   $62.61   $62.60   $62.60  
  Purchase #4 $233.91   8.448%   $253.6707   $253.67   $253.65   $253.70  
  Purchase #5 $60.51   10.457%   $66.8375   $66.84   $66.85   $66.80  
  Purchase #6 $145.60   9.749%   $159.7945   $159.79   $159.80   $159.80  
  Purchase #7 $107.57   8.115%   $116.2993   $116.30   $116.30   $116.30  
  7 purchase totals = $679.23       $735.7707   $735.77   $735.75   $735.80